1. Field of the Invention
This invention relates to storage mechanisms for flexible conduits and cables, and more particularly, to a vehicle mounted system for winding a flexible conduit or cable in a horizontal coil and automatically extending and retrieving cable responsive to vehicle movement.
2. Description of the Prior Art
Vehicles which are electrically powered through a multi-conductor umbilical chord are commonly used in underground mines. These vehicles are generally load-haul and dump type mining machines. One problem with such vehicles is the need to extend the cable as the vehicle moves forwardly and retract cable as the vehicle moves rearwardly. This function has generally been accomplished in the past by winding the cable on a reel or drum which is rotatably mounted on a transverse horizontal axis. The power is transferred from the cable to the vehicle drive motor through slip rings such as utilized by conventional AC motors. The slip rings must be custom designed to fit within the relatively small available volume. The reel is generally powered by an electric or hydraulic motor. The hydraulically powered varieties are generally either dual pressure systems or constant tension systems.
The dual pressure system continuously applies a torque to the reel, but the torque is lower for cable extension or a stationary condition than for cable retrieval. For proper functioning of the system the low torque setting must be large enough to keep excessive cable sag or slack from developing. The minimum cable tension is 100 pounds.
The constant tension system applies a constant torque to the reel. The value of the torque is not critical, but again it must be large enough to keep slack or sag from developing in the cable. The minimum cable tension for the constant tension system is 150 pounds. These conventional reel systems exhibit many problems which are alleviated by the inventive cable winding system. A principal problem with the prior art technique is the need to employ slip rings which quickly deteriorate in the severe environmental conditions of a mine. Additionally, the high inertia of the reel and particularly the cable wound thereon reduces the transient response of the cable retracting and extending system. Good transient response can only be maintained, then, by providing a fairly high cable tension. Yet, a relatively high cable tension in itself causes problems. As the cable is wound on the reel with a tension, the inward force exerted by the cable on the reel continues to build up thereby preventing the cable from being adequately cooled and excessively compressing the underlying cable. Also, the cable often catches on irregular contours in a mine, and the cable tension causes violent whipping of the cable as the cable is released, thereby posing a serious safety hazard. Cable whipping also occurs when the vehicle stops or reverses direction suddenly, although this problem is less severe with the constant tension system than the dual pressure system.
Another problem with conventional reel systems is that they must receive cable from the rear so that the cable is often severely damaged by backing over the cable with the vehicle. For these reasons, conventional vehicle mounted cable storage devices have not been entirely satisfactory.
Another approach to the problem of extending, retracting and storing umbilical cable in a mining vehicle is described in U.S. Pat. No. 3,990,551 issued to Jamison et al. The Jamison et al device includes a pair of selectively driven rollers engaging the cable therebetween. The rollers convey the cable to and from a rectangular storage box through a slot without guiding the cable in a specific arrangement. A constant torque is applied to the rollers thereby maintaining the tension in the cable constant. Thus the Jamison et al devices does not solve most of the above mentioned problems.